1. Field of the Invention
The present invention relates generally to a rotary actuator utilizing a solenoid. More particularly, this invention pertains to a rotary actuator having a rotor rotational range of not more than 180.degree..
2. Description of the Related Art
A rotary actuator is known which consists of a rotor having a permanent magnet fixed on a rotary shaft and a stator having poles disposed to oppose each other at an interval of 180.degree. with the rotary shaft therebetween (see, e.g., Japanese Unexamined Patent Publication No. 54-34013).
This type of rotary actuator has a stator consisting of a cylindrical coil bobbin with slots extending axially on the circumference thereof. A stator coil is axially wound around the coil bobbin and a cylindrical yoke is fitted to the circumference of the bobbin. The poles are formed to protrude from the internal circumference of the yoke.
The polarity of the poles may be changed by switching the direction that the stator coil is energized. This permits the rotor to be rotated under the magnetic interaction between the rotor and the stator. The described rotary actuator also has two stoppers for limiting the rotational range of the rotor.
However, the stator coil in the above rotary actuator has a hollow coil. That is, the center of the coil has an opening. This opening increases the magnetic reluctance which in turn reduces the magnetic flux density. Accordingly, the rotational torque provided is small relative to the coil current. Thus, a relatively large actuator must be used to provide a designate torque.
Such a rotary actuator suffers several other problems as well. To begin with, it requires the use of a winding machine having a complicated structure since the stator coil must be wound around the coil bobbin in the axial direction. Thus the assembly of the stator is troublesome. Further, the wires connected to the coil ends are easily detached since they are merely secured with an adhesive tape.
Further, the above actuator suffers the disadvantage that two stoppers are required and such stoppers cannot accurately regulate the rotational range of the rotor.